In 2016 the Department of Conservation received funding to control pigs in 7019 ha in Waipoua forest, Northland. Pigs are known to have detrimental effects on forest systems by potentially changing soil properties and affecting seedling turnover. Pigs may also be a vector of kauri phytophlera (Phytophlera agathidicida) and pig control is hoped to reduce the spread of kauri dieback and to protect kauri stands.
A pig control programme will start in earnest in June 2016 and it is proposed to control 7019 ha within Waipoua forest on an annual basis. Monitoring changes in pig disturbance is a requirement of the programme. It is unknown how any pigs are in the management area and there is likely to be high reinvasion of pigs from the surrounding forest. Monitoring changes to the proportion of pig disturbance (“rooting”) within the management area is one way to measure of the output of the control programme. Pig control and pig disturbance monitoring are not common in New Zealand and there are few good examples of robust monitoring programmes. This monitoring plan and sample design is largely based on pig disturbance monitoring undertaken by Auckland City in 16000ha of the Waitakere Ranges to monitor changes in response to a sustained programme of pig control (Krull, 2012 & Krull et al. (2016); Krull et al., 2013). Additional information will be collected on the hunting programme itself as a measure of the effort spent, such as the location and number of kills, hours and days spent hunting. Pig disturbance monitoring is planned to begin in June 2016 at the same time as pig control is planned to start. Pig disturbance monitoring is most sensitive in winter months because of the soft ground (Krull pers comm.).
Pig disturbance will be sampled by measuring the proportion of “fresh” and “old” pig disturbance along 8 - 10 permanently located transects in three monitoring “blocks” that are all nearly the same size to there is equal probabilities of selection between blocks so valid estimates for pig disturbance can be made.
Rules for transect establishment
When to abandon a sample point
Marking transects
See Appendix 1 and 2 for datasheets and examples of datasheets.
What to measure on transects
GPS and permanently mark the beginning of a transect and walk 100m at the random bearing that has already been allocated for each sample point. Look for evidence of pig disturbance 1m either side of the transect line (ie a 2m wide swath). When pig disturbance is observed, “project” the length of the disturbance onto the transect line and measure the length to the nearest 0.1m. See Figure 2 below (modified from Cheryl Krull). In this diagram there are two disturbance events. Disturbance 1 is 2.5m long and disturbance 2 is 1.2m long.
Figure 2. Demonstrating how to “project” the length of the disturbance on the transect and measure the length in metres to the nearest 0.1m.
Fresh vs Old disturbance
Figure 3. Fresh disturbance - moist and free of leaves.
Figure 4. Old disturbance - dried out and leaf litter present.
Figure 5. Old disturbance - presence of seedling growth in disturbance patch.
What else to record along transects (see Appendix 1 and 2)
The following resources are required;
To monitor the results of pig (Sus scrofa ) control in the core area of the pig management area in Waipoua Forest as part of efforts to control the spread of Kauri dieback disease.
A written description of the population intended for monitoring
Pig impacts in the Core Area of the Waipoua Forest Pig management Area
A spatial representation of the target population
Shapefile depicting the Core Area of the Waipoua pig management area
Monitoring transects have been located within the sample frame using the Balanced Acceptance Sampling (BAS) method. BAS allocates points in a spatially, balanced random order within the sample frame. Monitoring sites must be visited according to the spatially balanced sequence, the ‘sampleID’. In order to accomodate field constraints the Core Area sample frame has been divided into 3 roughly equal size areas and monitoring transects created in 3 ‘Groups’. Transects must be measured according to the order in the ‘sampleID’ in each ‘Group’. If a transect must be missed for reasons of access or safety then the next transcet in the ordered list must be used. 10 transects have been provided in each group as the initial sample. If needed, more transects are available from the oversample, although these must still be used according to the ordered list.
The transects from the sample and the oversample can be viewed below.
The shapefile for the transects can be downloaded below:
The data for the start and end point of the transects, including the random bearing, can be downloaded from the table below.
Pig disturbance in the core area of Waipoua Forest is low (0.58±2.51) when compared to the 3.7% measured by Krull (2012). Disturbance is clustered on 25% of the transects (Fig. 1). More years of data collection is required to assess change in pig disturbance levels as a result of pig culling efforts.
Figure 1. Distribution of pig disturbance and percent disturbance/transect on monitoring transects in Waipoua Forest.
Krull, C.R., 2012. Feral pigs in a temperate rainforest ecosystem: Ecological impacts and management (PhD thesis). ResearchSpace@ Auckland.
Krull, C.R., Choquenot, D., Burns, B.R., Stanley, M.C., 2013. Feral pigs in a temperate rainforest ecosystem: Disturbance and ecological impacts. Biological invasions 15, 2193–2204.
Krull, C.R., Stanley, M.C., Burns, B.R., Choquenot, D., Etherington, T.R., 2016. Reducing wildlife damage with cost-effective management programmes. PloS one 11.